water flow issue

i have an issue with the water flow in my system. from this picture you can see that there are 6 (1200 gallon) tanks. the water exits the bottom of the tanks and flows to the sump tank all the way end (the smaller tank on the right at the back of the photo). i have been running the system for over a year now and i am running into a problem.

as i get further from the sump tank the level of the water seems to get higher. i am wondering if the pressure from the tanks down the line is restricting the water flow from the earlier tanks? would i be better off to have three inlets into the sump tank (one from tanks (1 and 2) one from tanks (3 and 4) and one from tanks (5 and 6)) or will i just end up with the same issue?

Yea as you add more tanks you would either need to adjust the flow rates to suit the drain plumbing or increase the size of the drain plumbing to handle more flow or perhaps simpler to run more drain lines to handle it.

IMHO your are probably getting equal flow from each of the six tanks. The higher water level as you get further from the sump would indicate a higher pressure at the farthest tank to compensate for the friction losses for the additional length of pipe getting back to the sump.

Chris friction loss due to distance or length of pipe, debri and algae on the inside of you pipe is the cause for sure. I would caution against different flow rates into the fish tanks. You should be close as possible. A quick fix is to add a second main drain to the end of line and run it all the way back to the other end and connect, effectively doubling your main drain line. If one fish tank gets 20 gpm and the end gets 12 you can see fish load would build up in the end tanks. Just a thought.